Why would you want greasy fingerprints all over your display and gorilla arm syndrome when there's a perfectly fine keyboard and touchpad attached to the display for free?
No reason for gorilla-arm when touch is an alternative interaction mode and not a required one. You still have trackpad and keyboard. You can dynamically switch modes depending on the action.
Gorilla-arm was a fear based on the naive idea that if you had touch, you would be required to only use touch for every action.
Is apple going to be so restrained to keep the design of the OS as a mouse first experience or are they going to cripple information density so I might be able to close a window with my elbow?
People act as if Chromebooks with touch screens aren't already considered a huge UX upgrade over Chromebooks without. Use your finger where it makes sense and the mouse where it doesn't. Literally nobody gets tripped up over this in practice.